PTL 1, PTL 2 and PTL 3 disclose processes in which a wet mixed sheet obtained by making paper from a paper material containing uniformly mixed heat-expanding particles is dried and simultaneously expanded in a drying step, to obtain a homogeneous bulky paper with a density of 0.1-0.3 g/cm3, and having no concavo-convex pattern. PTL 4 discloses a process for producing a sheet with a concavo-convex pattern obtained by thermal expansion of heat-expanding particles. Specifically, PTL 4 discloses anchoring heat-expanding particles in pulp and then aggregating them to form flock, dispersing the flock in a paper material containing no heat-expanding particles and making a paper, and then heating the obtained sheet to cause expansion of the heat-expanding particles to form a patterned sheet with a concavo-convex pattern wherein the flock-containing sections have become the expanded bulky sections.